From 5f8de423f190bbb79a62f804151bc24824fa32d8 Mon Sep 17 00:00:00 2001 From: "Matt A. Tobin" Date: Fri, 2 Feb 2018 04:16:08 -0500 Subject: Add m-esr52 at 52.6.0 --- security/sandbox/chromium/base/memory/weak_ptr.h | 345 +++++++++++++++++++++++ 1 file changed, 345 insertions(+) create mode 100644 security/sandbox/chromium/base/memory/weak_ptr.h (limited to 'security/sandbox/chromium/base/memory/weak_ptr.h') diff --git a/security/sandbox/chromium/base/memory/weak_ptr.h b/security/sandbox/chromium/base/memory/weak_ptr.h new file mode 100644 index 000000000..33d1e4736 --- /dev/null +++ b/security/sandbox/chromium/base/memory/weak_ptr.h @@ -0,0 +1,345 @@ +// Copyright (c) 2012 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +// Weak pointers are pointers to an object that do not affect its lifetime, +// and which may be invalidated (i.e. reset to NULL) by the object, or its +// owner, at any time, most commonly when the object is about to be deleted. + +// Weak pointers are useful when an object needs to be accessed safely by one +// or more objects other than its owner, and those callers can cope with the +// object vanishing and e.g. tasks posted to it being silently dropped. +// Reference-counting such an object would complicate the ownership graph and +// make it harder to reason about the object's lifetime. + +// EXAMPLE: +// +// class Controller { +// public: +// Controller() : weak_factory_(this) {} +// void SpawnWorker() { Worker::StartNew(weak_factory_.GetWeakPtr()); } +// void WorkComplete(const Result& result) { ... } +// private: +// // Member variables should appear before the WeakPtrFactory, to ensure +// // that any WeakPtrs to Controller are invalidated before its members +// // variable's destructors are executed, rendering them invalid. +// WeakPtrFactory weak_factory_; +// }; +// +// class Worker { +// public: +// static void StartNew(const WeakPtr& controller) { +// Worker* worker = new Worker(controller); +// // Kick off asynchronous processing... +// } +// private: +// Worker(const WeakPtr& controller) +// : controller_(controller) {} +// void DidCompleteAsynchronousProcessing(const Result& result) { +// if (controller_) +// controller_->WorkComplete(result); +// } +// WeakPtr controller_; +// }; +// +// With this implementation a caller may use SpawnWorker() to dispatch multiple +// Workers and subsequently delete the Controller, without waiting for all +// Workers to have completed. + +// ------------------------- IMPORTANT: Thread-safety ------------------------- + +// Weak pointers may be passed safely between threads, but must always be +// dereferenced and invalidated on the same SequencedTaskRunner otherwise +// checking the pointer would be racey. +// +// To ensure correct use, the first time a WeakPtr issued by a WeakPtrFactory +// is dereferenced, the factory and its WeakPtrs become bound to the calling +// thread or current SequencedWorkerPool token, and cannot be dereferenced or +// invalidated on any other task runner. Bound WeakPtrs can still be handed +// off to other task runners, e.g. to use to post tasks back to object on the +// bound sequence. +// +// If all WeakPtr objects are destroyed or invalidated then the factory is +// unbound from the SequencedTaskRunner/Thread. The WeakPtrFactory may then be +// destroyed, or new WeakPtr objects may be used, from a different sequence. +// +// Thus, at least one WeakPtr object must exist and have been dereferenced on +// the correct thread to enforce that other WeakPtr objects will enforce they +// are used on the desired thread. + +#ifndef BASE_MEMORY_WEAK_PTR_H_ +#define BASE_MEMORY_WEAK_PTR_H_ + +#include "base/base_export.h" +#include "base/logging.h" +#include "base/macros.h" +#include "base/memory/ref_counted.h" +#include "base/sequence_checker.h" +#include "base/template_util.h" + +namespace base { + +template class SupportsWeakPtr; +template class WeakPtr; + +namespace internal { +// These classes are part of the WeakPtr implementation. +// DO NOT USE THESE CLASSES DIRECTLY YOURSELF. + +class BASE_EXPORT WeakReference { + public: + // Although Flag is bound to a specific SequencedTaskRunner, it may be + // deleted from another via base::WeakPtr::~WeakPtr(). + class BASE_EXPORT Flag : public RefCountedThreadSafe { + public: + Flag(); + + void Invalidate(); + bool IsValid() const; + + private: + friend class base::RefCountedThreadSafe; + + ~Flag(); + + SequenceChecker sequence_checker_; + bool is_valid_; + }; + + WeakReference(); + explicit WeakReference(const Flag* flag); + ~WeakReference(); + + bool is_valid() const; + + private: + scoped_refptr flag_; +}; + +class BASE_EXPORT WeakReferenceOwner { + public: + WeakReferenceOwner(); + ~WeakReferenceOwner(); + + WeakReference GetRef() const; + + bool HasRefs() const { + return flag_.get() && !flag_->HasOneRef(); + } + + void Invalidate(); + + private: + mutable scoped_refptr flag_; +}; + +// This class simplifies the implementation of WeakPtr's type conversion +// constructor by avoiding the need for a public accessor for ref_. A +// WeakPtr cannot access the private members of WeakPtr, so this +// base class gives us a way to access ref_ in a protected fashion. +class BASE_EXPORT WeakPtrBase { + public: + WeakPtrBase(); + ~WeakPtrBase(); + + protected: + explicit WeakPtrBase(const WeakReference& ref); + + WeakReference ref_; +}; + +// This class provides a common implementation of common functions that would +// otherwise get instantiated separately for each distinct instantiation of +// SupportsWeakPtr<>. +class SupportsWeakPtrBase { + public: + // A safe static downcast of a WeakPtr to WeakPtr. This + // conversion will only compile if there is exists a Base which inherits + // from SupportsWeakPtr. See base::AsWeakPtr() below for a helper + // function that makes calling this easier. + template + static WeakPtr StaticAsWeakPtr(Derived* t) { + typedef + is_convertible convertible; + static_assert(convertible::value, + "AsWeakPtr argument must inherit from SupportsWeakPtr"); + return AsWeakPtrImpl(t, *t); + } + + private: + // This template function uses type inference to find a Base of Derived + // which is an instance of SupportsWeakPtr. We can then safely + // static_cast the Base* to a Derived*. + template + static WeakPtr AsWeakPtrImpl( + Derived* t, const SupportsWeakPtr&) { + WeakPtr ptr = t->Base::AsWeakPtr(); + return WeakPtr(ptr.ref_, static_cast(ptr.ptr_)); + } +}; + +} // namespace internal + +template class WeakPtrFactory; + +// The WeakPtr class holds a weak reference to |T*|. +// +// This class is designed to be used like a normal pointer. You should always +// null-test an object of this class before using it or invoking a method that +// may result in the underlying object being destroyed. +// +// EXAMPLE: +// +// class Foo { ... }; +// WeakPtr foo; +// if (foo) +// foo->method(); +// +template +class WeakPtr : public internal::WeakPtrBase { + public: + WeakPtr() : ptr_(NULL) { + } + + // Allow conversion from U to T provided U "is a" T. Note that this + // is separate from the (implicit) copy constructor. + template + WeakPtr(const WeakPtr& other) : WeakPtrBase(other), ptr_(other.ptr_) { + } + + T* get() const { return ref_.is_valid() ? ptr_ : NULL; } + + T& operator*() const { + DCHECK(get() != NULL); + return *get(); + } + T* operator->() const { + DCHECK(get() != NULL); + return get(); + } + + // Allow WeakPtr to be used in boolean expressions, but not + // implicitly convertible to a real bool (which is dangerous). + // + // Note that this trick is only safe when the == and != operators + // are declared explicitly, as otherwise "weak_ptr1 == weak_ptr2" + // will compile but do the wrong thing (i.e., convert to Testable + // and then do the comparison). + private: + typedef T* WeakPtr::*Testable; + + public: + operator Testable() const { return get() ? &WeakPtr::ptr_ : NULL; } + + void reset() { + ref_ = internal::WeakReference(); + ptr_ = NULL; + } + + private: + // Explicitly declare comparison operators as required by the bool + // trick, but keep them private. + template bool operator==(WeakPtr const&) const; + template bool operator!=(WeakPtr const&) const; + + friend class internal::SupportsWeakPtrBase; + template friend class WeakPtr; + friend class SupportsWeakPtr; + friend class WeakPtrFactory; + + WeakPtr(const internal::WeakReference& ref, T* ptr) + : WeakPtrBase(ref), + ptr_(ptr) { + } + + // This pointer is only valid when ref_.is_valid() is true. Otherwise, its + // value is undefined (as opposed to NULL). + T* ptr_; +}; + +// A class may be composed of a WeakPtrFactory and thereby +// control how it exposes weak pointers to itself. This is helpful if you only +// need weak pointers within the implementation of a class. This class is also +// useful when working with primitive types. For example, you could have a +// WeakPtrFactory that is used to pass around a weak reference to a bool. +template +class WeakPtrFactory { + public: + explicit WeakPtrFactory(T* ptr) : ptr_(ptr) { + } + + ~WeakPtrFactory() { + ptr_ = NULL; + } + + WeakPtr GetWeakPtr() { + DCHECK(ptr_); + return WeakPtr(weak_reference_owner_.GetRef(), ptr_); + } + + // Call this method to invalidate all existing weak pointers. + void InvalidateWeakPtrs() { + DCHECK(ptr_); + weak_reference_owner_.Invalidate(); + } + + // Call this method to determine if any weak pointers exist. + bool HasWeakPtrs() const { + DCHECK(ptr_); + return weak_reference_owner_.HasRefs(); + } + + private: + internal::WeakReferenceOwner weak_reference_owner_; + T* ptr_; + DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory); +}; + +// A class may extend from SupportsWeakPtr to let others take weak pointers to +// it. This avoids the class itself implementing boilerplate to dispense weak +// pointers. However, since SupportsWeakPtr's destructor won't invalidate +// weak pointers to the class until after the derived class' members have been +// destroyed, its use can lead to subtle use-after-destroy issues. +template +class SupportsWeakPtr : public internal::SupportsWeakPtrBase { + public: + SupportsWeakPtr() {} + + WeakPtr AsWeakPtr() { + return WeakPtr(weak_reference_owner_.GetRef(), static_cast(this)); + } + + protected: + ~SupportsWeakPtr() {} + + private: + internal::WeakReferenceOwner weak_reference_owner_; + DISALLOW_COPY_AND_ASSIGN(SupportsWeakPtr); +}; + +// Helper function that uses type deduction to safely return a WeakPtr +// when Derived doesn't directly extend SupportsWeakPtr, instead it +// extends a Base that extends SupportsWeakPtr. +// +// EXAMPLE: +// class Base : public base::SupportsWeakPtr {}; +// class Derived : public Base {}; +// +// Derived derived; +// base::WeakPtr ptr = base::AsWeakPtr(&derived); +// +// Note that the following doesn't work (invalid type conversion) since +// Derived::AsWeakPtr() is WeakPtr SupportsWeakPtr::AsWeakPtr(), +// and there's no way to safely cast WeakPtr to WeakPtr at +// the caller. +// +// base::WeakPtr ptr = derived.AsWeakPtr(); // Fails. + +template +WeakPtr AsWeakPtr(Derived* t) { + return internal::SupportsWeakPtrBase::StaticAsWeakPtr(t); +} + +} // namespace base + +#endif // BASE_MEMORY_WEAK_PTR_H_ -- cgit v1.2.3